1. Field of the Invention
The present invention relates to a transfer unit transferring a platelike workpiece such as a semiconductor wafer from or to a cassette.
2. Description of the Related Art
In recent years, it has been desired to reduce the thickness of a wafer such as a silicon wafer by grinding for realization of device chips reduced in size and weight. For example, this grinding is performed by using a grinding apparatus including a chuck table holding the wafer under suction and a grinding wheel provided above the chuck table, the grinding wheel having a plurality of abrasive members grinding the upper surface of the wafer held on the chuck table. In operation, both the chuck table and the grinding wheel are rotated and the grinding wheel is lowered to bring the abrasive members into contact with the upper surface (work surface) of the wafer, thereby grinding the upper surface of the wafer to thereby reduce the thickness of the wafer.
In the case of cutting the wafer reduced in thickness and accordingly reduced in rigidity by using a cutting blade or the like to divide the wafer into a plurality of device chips, a problem such as chipping and cracking of the wafer tends to occur. To cope with this problem, there has recently been put into practical use a processing method including the steps of applying a laser beam having a wavelength hardly absorptive to a wafer in the condition where the laser beam is focused inside the wafer, thereby forming a modified layer as a break start point inside the wafer, and next grinding the wafer (see PCT Patent Publication No. WO03/077295, for example). In this processing method, an external force applied to the wafer in grinding is used to divide the wafer into a plurality of device chips as reducing the thickness of the wafer. Accordingly, it is unnecessary to cut the wafer reduced in rigidity.